Since the gain of a given amplifier is limited, a desired rate of amplification of a microwave signal often requires the use of two amplifiers connected in parallel whose output signals are then additively combined. These amplifiers are generally connected to respective outputs of a power divider, e.g. a hybrid junction of the Magic-T type, by which they are cophasally energized. If a phase shift should occur in the two signal paths containing these amplifiers, some of the power will be lost in the adder stage. Moreover, a breakdown of either amplifier necessitates its disconnection from the circuit with the aid of switches controlled by signal monitors in the adder. Even with fast-acting electronic switches, however, an unavoidable signal interruption of finite duration will occur during such disconnection.